I've tried two things that seem to work very well for me. First, I have all my water ready, but separate about 4 oz and warm it slightly. I put the entire amount of salt in the warmed water and mix it until it dissolves. Then I just drink that portion as a quick 'shot.' Then I immediately drink the rest of the room temperature water. It seems to keep me from feeling like vomiting.
Also, I have done just 1/2 dose of the swf for a couple days until I get more used to it. I still get lots of good elimination, I'm a smaller person so that could be why. This also keeps me from feeling like I will vomit.